In a typical furnace black process, a carbonaceous feed is introduced into a reactor and contacted with hot combustion gas which elevates the temperature of the feed to a temperature sufficiently high to decompose the feed to form particulate carbon black entrained in hot gas, the admixture referred to as reactor effluent or smoke. Such combustion products are typically at a temperature in the range of about 2400.degree. F. to about 2900.degree. F. The reactor effluent is cooled, usually by introducing a quench fluid into the smoke, to form an effluent containing particulate carbon black. The effluent is subsequently separated into a gas phase and a particulate carbon black phase by separating means such as a cyclone separator, bag filters, or the like. However, prior to the filtering or separation step the effluent should be cooled to a temperature sufficiently low to prevent damage to the separating means. A plurality of cooling steps can be employed.
It is common practice to initially cool or quench the reactor effluent by injecting directly thereinto quench fluid at one or more points in the quench chamber portion of the reactor. Typical quench fluids include water, cooled effluent or smoke, and/or off-gas, off gas being a portion of the gas phase separated from the effluent. Such a first cooling step normally lowers the temperature of the reactor effluent to a temperature of about 2000.degree. F. or less and preferably between about 1600.degree. and 2000.degree. F. The first cooling is done to lower the temperature of the combustion products to a temperature which can be especially accommodated in an indirect heat exchange means and to a temperature below which no further production of carbon black occurs.
The second step of cooling involves the use of a first indirect heat exchange means, such as a shell-tube heat exchanger which further lowers the temperature of the effluent to a temperature of about 1200.degree. F. or less and preferably between about 800.degree. F. and about 1200.degree. F. The thusly cooled effluent can then be passed to one or more economizers, e.g., indirect heat exchangers which are operable for heating air and/or carbonaceous feedstock to be introduced into the reactor. It is also common practice in the art when necessary to finally cool the effluent by injecting a trim quench fluid into the effluent before separating effluent into carbon black and off-gas. The final cooling lowers the temperature of the effluent to a temperature which can be especially accommodated by the separating means. Typically, this temperature would be below about 600.degree. F. for bag filters. However, this temperature is dependent upon the type of bag filters or the type of separating means used. However, one problem encountered is that carbon black deposits tend to build up in the first indirect heat exchanger. A thin layer of the carbon black will substantially lower the heat transfer rate in the indirect heat exchanger. To clean the indirect heat exchanger to maintain high heat transfer rates, the reactor can be shut down and allowed to cool to a temperature at which the indirect heat exchanger can be partially disassembled for cleaning by methods well known in the art to remove carbon black deposits. However, such a cleaning method is wasteful, as the apparatus must be shut down to effect the cleaning and the indirect heat exchanger must be partially disassembled for cleaning. After the cleaning operation, the apparatus is placed back in operation and allowed a period of operating time which can be several hours to stablize before the production of carbon black is commenced. Such a method is wasteful of man hours, fuel, and production time.
The present invention provides a method and apparatus for producing carbon black which minimizes carbon black deposits in the indirect heat exchanger and, at the same time, maximizes the heat transfer efficiency without the aforementioned problems.
Accordingly, an object of this invention is to provide a method of producing carbon black which can be operated substantially continuously without need of completely terminating operations for cleaing of an indirect heat exchanger to maintain the desired high heat transfer rate.
A further object of this invention is to provide an apparatus to accomplish such a method.
Other objects, aspects, as well as the several advantages of the present invention will become apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawing and the appended claims.